Field of the Invention
The present invention relates to a technique of improving throughput in TCP communication.
Description of the Related Art
The Transmission Control Protocol (TCP) is widely known as a protocol for performing congestion control in Internet communication. TCP is described in documents such as RFC 793, RFC 1122, RFC 2581, and RFC 2582, and subjected to continuous research for improvements. TCP uses automatic repeat request (ARQ) for error control. In ARQ, the sender transmits a data packet to the receiver, and the receiver that has received the data packet transmits an acknowledgement (ACK) packet to the sender. If no ACK packet has been received in response to the data packet, the sender re-transmits the data packet. Moreover, the sender tries to transmit a plurality of packets within a fixed size at once, in order to increase throughput. Such control is called sliding window flow control. This control is designed to gradually increase throughput to avoid network congestion.
In recent years, an increasing number of mobile communication terminals have been provided with high-speed communication schemes. Meanwhile, power saving has been promoted, too. Despite the capability of high-speed communication, communication delay jitter or sudden delays tend to occur due to power saving. When a sudden delay occurs, the reception of the ACK packet is delayed, so that the sender re-transmits the data packet. Besides, having re-transmitted the data packet, the sender determines that the network is congested, and performs control to decrease throughput. This causes lower throughput. To deal with such a sudden delay in a wireless environment, for example, Japanese Patent Laid-Open No. 2006-5833 discloses a technique of determining whether or not a temporal variation occurs based on network characteristic information and controlling the value of a congestion control variable.
However, appropriate communication control cannot be performed merely by determining whether or not a temporal variation occurs based on network characteristic information as described in Japanese Patent Laid-Open No. 2006-5833. For example, the above-mentioned power saving characteristic information of the communication terminal or control information relating to the operating system (OS) of the communication terminal are unable to be utilized.